In the process of developing, certifying and deploying wireless transceivers such as communications devices, it is necessary to test performance at various points along the way. This testing can be both to assure that the communications system meets its intended purpose and performance, and to be sure it does not interfere with other wireless devices that share the RF spectrum.
The criticality of this testing process is well illustrated by the activities in the cognitive radio (CR) technology area. Cognitive Radios are wireless transceivers that sense spectrum usage by primary users (PU), and adapt their transmission to utilize unused and under used spectrum to communicate. CR technology is not likely to be widely deployed until the degree of primary user disruption can be accurately known and kept to acceptable levels with acceptable CR performance. CR performance and interaction with primary users is very difficult to measure and model because of many factors including the potential for large numbers of participating nodes, breadth of scenarios and environments, and adaptation/cognitive nature of the CR nodes.
To create a context for describing the unique attributes of the presently disclosed test bed, the current state of the art will be summarized. At the two ends of the “test bed spectrum” are full featured field tests and software-based modeling.
Full-featured field tests place the wireless transceivers in a field scenario containing some representative RF environment where they will be operated while test data is collected. These sorts of tests are often expensive and complex to orchestrate, and can lack flexibility since mixes of test transceiver numbers/types/locations, incumbent RF user numbers/types/locations and RF propagation conditions cannot be systematically varied to collect comprehensive data. FIG. 1 schematically depicts a typical field test equipment setup. Wireless Transceiver Units Under Test (UUT) 100 operate in some RF environment 110. The RF emissions are subject to the noise, path loss, multipath transmission and interferers found in the local RF environment. Test instrumentation 120 is established to measure the performance of the UUT and other PU of the RF environment. In order to accomplish a field test of this variety, the UUT must be physically located in the test RF environment, and test instrumentation must be constructed. In order to vary the numbers/types/locations of UUT and PU, physical units must be acquired and placed in the RF environment. In order to vary the RF environment, different field venues must be available. Additionally, test instrumentation must be provided and adapted for each UUT/PU/test environment scenario where testing is to be accomplished.
Lab-based testing using cable-based interconnection for RF emissions of UUT and the RF environment is a prior art approach to testing to overcome the challenges of placing and monitoring devices in the field environment. FIG. 2 depicts a typical lab-based equipment setup. As in field testing, Wireless Transceiver Units Under Test (UUT) 100 are acquired and instrumented with Test Instrumentation 120. Instead of the RF environment being that found in the field, RF test equipment such as signal generators are used to produce Interferers 210, Noise Generators 220, and Path Simulators 200 to simulate path loss and multipath in an RF channel, RF Interconnection 230 is accomplished using RF cables such as coaxial cables. This test set up approach reduces some of the complexities of field testing, but introduces new concerns over RF environment realism. Further, it still requires the physical introduction of new UUT and RF test equipment into the configuration for comprehensive transceiver configuration and RF environment results.
A variation on RF cable-connected lab testing has become more prevalent and straightforward as wireless transceiver devices have tended towards digital waveforms and digital hardware or software implementation. FIG. 3a depicts a typical framework for modern wireless communications devices as defined by the prior art OSI model. Here, different functions in the Wireless Transceiver 100 are allocated to layers in the functional stack 300. The physical layer in stack 300 is where the waveform-related functionality is contained. The physical layer can be segregated into a digital implementation portion 310 and an analog portion 320. Typical functions in the digital portion 310 are waveform generation 330 and digital to analog conversion 340. Typical functions found in the analog portion 320 are baseband to RF conversion 350. Other digital processing functions associated with non-physical layers (2 through 7) are contained in the digital data processing block 360. The functions listed (330, 340, 350, 360) are found in the transmit side of the transceiver. Equivalent functions are found in the receive side such as RF to baseband conversion, analog to digital conversion, and waveform processing to recover information. Given this decomposition of functionality, the UUT can be conveniently implemented in an RF cable-interconnected lab test bed as shown in FIG. 3b. With reference to FIG. 3b, the UUT is shown implemented in three physical entities; an embedded PC 385 to accomplish Layer 2-7 functionality (“digital data processing” from FIG. 3a), a Universal Software Radio Peripheral (USRP) 380 performing the physical layer digital functions (“digital waveform generation” and “digital to analog conversion” from FIG. 3a), and an RF Module, 375 to perform the physical layer analog functions (“baseband to analog conversion” from FIG. 3a). FIG. 3b also introduces a Primary User Simulator, 370 as a piece of RF test equipment to simulate the existence and characteristics of other users sharing the same channel.
Testing using software-based modeling is economical and flexible, but generally falls short in incorporating real world effects, especially in the area of the wireless environment. These shortcomings contribute to the inability to convincing stake holders of the CR-primary user interaction. This is especially true given the nature of the primary users, many of whom purchased exclusive rights to use the spectrum. Software-based modeling has become more prevalent and straightforward as wireless transceiver devices have tended towards digital waveforms and digital hardware or software implementation.
As previously described, FIG. 3a depicts a reference framework for modern wireless communications devices as defined by the prior art OSI model. Here, different functions in the Wireless Transceiver 100 are allocated to layers in the functional stack 300. Many software-based test beds with different relevant attributes exist today.
FIG. 3c depicts another prior art test-bed, Computer-based hardware hosts a software-based test platform 325 to provide a framework for the software model-based transceiver testing application. In FIG. 3c, multiple UUT 100 are shown with their OSI model stacks 300. Test instrumentation functionality 120 serving the same general purpose as in prior test bed architectures is also shown. As these UUT generally adhere to the OSI model, and are digital in nature, they can be “interconnected” to test functionality at different layers in the OSI stack as shown 315. For example, UUT #1 and UUT #n can be interconnected at the network, data link or digital physical layer for testing. Completeness and field validity of the testing decreases as the interconnection of the software-modeled UUT moves away from the physical layer. Two major shortcomings in the software model testing approach can be gleaned. First, since the test bed is entirely software based, and therefore digital, the analog RF effects are not taken into account and are not tested. Some test bed architectures may enhance the testing by simulating effects of the RF channel in the interconnection function 315. Including the important RF channel parameters is difficult and resource stressing in most cases. The second shortcoming is that the UUT models may be required to operate in non-real time. In other words, they operate in accordance with the execution speed of the software model, which are not necessarily the actual physical UUT speeds. This means that time related physical parameters such as waveform time of arrival/frequency of arrival related to distances between nodes, or rendezvous times where two UUT are tuned to the same RF frequency may not be accurately modeled.
Many lab-based test beds examples exist today that vary from wired RF interconnections of physical devices to software-model based simulations. A sample list includes:                Georgia Tech University Test Bed—Multiple primary networks (non-programmable), CRN with flexibility for multiple CR types, lab-based with unrealistic channel model        Virginia Tech Genetic Algorithm Test bed—Wireless link carrying video as CR, fixed function wireless interferer, lab wireless environment        MIRAI Cognitive Radio Execution Framework (MIRAI-CREF)—a scalable multi-thread simulation core supporting parallel execution capable of integrating with real physical devices, but over a wired network        IRIS (Implementing Radio in Software), developed by CTVR (CTVR, Trinity College, Dublin, Ireland), a suite of software components that implement various functions of wireless communications systems. A system for managing the structure and characteristics of the components and signal chain. 2 GHz OFDM platform.        The Kansas University Agile Radio (KUAR) platform is a low cost, flexible RF, small form factor SDR implementation that is both portable and computationally powerful. This platform features a flexible-architecture RF front-end that can support both wide transmission bandwidths and a large center frequency range, a self-contained, small form factor radio unit for portability, a powerful on-board digital processing engine to support a variety of cognitive functions and radio operations, and a low cost build cycle to easily facilitate broad distribution of the radio units to other researchers within the community. The KUAR platform was demonstrated at IEEE DySPAN 2007 in Dublin, Ireland. This demonstration involved an OFDM-based link operating in the 5 GHz band [2].        The Winlab facility at Rutgers is an initiative to develop a novel cognitive radio hardware prototype for research on adaptive wireless networks. This is a network-centric cognitive radio architecture aimed at providing a high performance networked environment where each node may be required to carry out high throughput packet forwarding functions between multiple physical layers. Key design objectives for the cognitive radio platform include:                    multi-band operation, fast frequency scanning, and agility;            software-defined modem including waveforms such as DSSS/QPSK and OFDM operating at speeds up to 50 Mbps;            packet processor capable of ad-hoc packet routing with aggregate throughput ˜100 Mbps;            spectrum policy processor that implements etiquette protocols and algorithms for dynamic spectrum sharing.                        Rockwell Collins—Software Defined Radio Software Communications Architecture Waveform Development System (SCA WDS). The Rockwell Collins SDR WDS includes the FlexNet 2 MHz to 2 GHz multi-channel SDR. The FlexNet Four offers enhanced capacities to significantly improve the connectivity, mobility, versatility, interoperability and exchange of information on the battlefield.        University of California, Berkeley—Test bed based on BEE2, a multi-FPGA emulation engine, fixed or flexible function primary nodes, flexible function CR nodes, lab-based with unrealistic wireless channel model, fixed 2.4 GHz RF band (85 MHZ BW)        Virginia Tech OSSIE/Tektronix Test Equipment CORTEKS—CR node based on OSSIE with Tektronix RF test equipment for primary node(s), lab radio environment        Open Access Research Testbed for Next-Generation Wireless Networks (ORBIT)—an open-access experimental environment to evaluate protocols and the performance of applications in real-world settings utilizing a radio-grid emulator that consists of radio nodes such as 802.11a/b/g and cognitive radio devices, includes an option for physical radio devices with lab wireless environment.        DARPA XG field testbed-small-scale, rural terrain, spectrum overlay realization.        NSF GENI Program (large Cog radio testbed)        NSF ERC program        DARPA IAMANET        VA Tech ICTAS VT CORNET (based on USRP II connected to an embedded PC)—30 nodes with some mobility, GNU radio based, campus test bed only.        Carnegie Mellon Radio Test bed—Provides for real-time physical layer emulation for RF propagation for multiple 802.11 radios (not CR test bed, no emulation of primary/secondary user interaction, uses DSP hardware and FPGAs for channel emulation)        OMesh Networks—Zigbee based commercial wireless mesh cognitive networking system. Supports up to 250 kbps data rates for voice, low-rate video, and data.        NTRG Software Radio Test bed—Networks and Telecommunications Research Group, Trinity College, Dublin, Ireland.        
In reviewing the characteristics of these test beds, a set of attributes has been identified that illustrate shortcomings in comprehensive, realistic and efficient testing. These desirable attributes include:                Support wide RF bandwidths—assesses the test bed hardware capability to simulate/operate in both wide-band RF (greater than approximately several MHz), and supports multiple RF bands (separated by tens of MHz). This feature is required for testing the spectrum sensing functionality in a CR to support dynamic spectrum access (DSA) within a particular band so as to avoid interference and primary band users.        Support networked wireless transceivers—Many prior art test beds operate with one or a few nodes in “stand-alone” mode, including CR nodes.        Portable Transceivers—In many surveyed test beds, the test bed contains non-portable equipment such as test-equipment grade components (signal generators, spectrum analyzers, arbitrary waveform generators, etc). While this can be sufficient for lab testing, it is not suitable to be used in a field environment, which limits the utility of the test bed. A desirable test bed attribute would be where the UUT could be exercised in the lab environment with controlled primary/secondary spectrum conditions and simulated physical motion, and then brought into real-world conditions of a live RF environment where it can be exercised and analyzed under less controlled scenarios to provide irrefutable and necessary demonstrations of performance.        Scalable—While in theory any test bed is scalable, in that the size of the test bed could be made arbitrarily large and complex. However, many test beds surveyed utilize lab-grade test equipment or other highly expensive components that make these systems not realistically scalable. In order to emulate an arbitrarily large number of PU and UUT, it would not be cost effective or easily manageable to use tens or hundreds of users in the form of lab test equipment.        MIMO capable (multi-antenna)—MIMO is considered to be one of the most promising new advances in spectral efficiency seen in recent communications systems. As such, it is being included as a base capability in new wireless standards. Therefore, MIMO capable hardware, supporting multiple phase coherent antennas for beamforming, spatial multiplexing, and de-multiplexing, and associated propagation channel models, is a required component of a comprehensive test bed.        Multiple Realistic Wireless Channel Models—Many test beds do not offer this basic capability. Many test beds utilize either a simple AWGN channel or have a limited channel simulation or emulation capability, enabled by either software fading algorithms or through highly expensive RF fading channel simulators which offer point to point signal manipulation (such as Rayleigh fading, multipath, Doppler shift, etc) on only a few sources.        Waveforms Flexibility—Nearly all surveyed test beds offer very limited scope of testing and are geared to a single specific application. A full featured test bed should offer to provide a test capability for an arbitrary number of PU and UUT.        Industry Standard Hardware Interfaces—Utilizing non-proprietary hardware interfaces provides a much more flexible way to test a multitude of potentially different hardware devices in the same test bed. If the main functions, low-level signal processing, and interfaces to the RF are developed around well-defined and standardized APIs, hardware interfaces, and hardware abstraction layers, it will be much simpler to break apart the components and exercise them as either physical or virtual entities in the test bed. This will also enable a simpler mechanism to substitute different RF modules with different RF band capabilities into the test bed.        Incorporates Geolocation—None of the surveyed test beds incorporate the ability to provide precision geolocation of detected spectrum users, which is considered to be an inherent weakness in the effort to develop powerful and effective wireless devices.        Realtime/Non-realtime—Many surveyed test beds have focused on a real-time capability, which can distract from the purpose of the testing. An approach where both the UUT and the channel are synchronous, but running in either real time or non-real time, satisfies the ability to measure performance and more importantly, one could simulate a huge number of primary and secondary users, very complex channel effects, etc, without extensive hardware resources.        Faithfully emulate an RF Environment vs. a Propagation Path based on Range—some laboratory test beds have the ability to accurately emulate an RF path between UUT based on range, but do not emulate the path delay or any other features of a realistic RF environment such as physical environment or other co-spectrum transmitters or receivers.        Allow testing of a variety of RF systems—RF test beds tend to be oriented towards testing of one variety of RF systems (such as communications systems) vs. allow testing of sensing RF systems (such as radars) or navigation systems (such as GPS), or other types of RF systems.        
Based on this sample set and a plethora of other test beds that exist in industry and academia, a wireless transceiver test bed approach that produces broadly applicable realistic results, and yet is scalable, flexible and affordable does not exist.
The present disclosure utilizes emerging technologies and trends in the areas of digital signal processing, wireless device design, wideband networks, computer and software architecture/capability and software-based modeling to provide a means to address these shortcomings. Specific technology innovations include:                digital signal processing power and available algorithms and models        ability to digitize RF and convert digital signals to RF with high fidelity        emerging software defined radio (SDR) software architectures, such as SCA (Software Communications Architecture)        emerging commercial off-the-shelf digital radio and SDR components (hardware and software)        ever increasing broadband connectivity between distributed sites        comprehensive and advanced RF propagation models        RF transceiver models being built in software        proliferation of radio functionality being digital and implemented in software with discrete events (bits, bursts, frames, etc.).        standardization of baseband digitized interfaces to SDRs (such as the VITA-49 Radio Transport Protocol)        proliferation of widely available high-speed computer data interfaces (such as PCI-Express 2.0) for exchanging large volumes of data between processing elements with low latency and high throughput        
The present disclosure is not limited to wireless devices in the application area of communications, but broadly applies to all wireless devices and networks including receive only, transmit only and diverse applications such as sensing, radar, navigation and jamming.